Fix MSVC build
std::unary_function
has been deprecated in C++11, and has not been needed anyway.
Failed job: https://github.com/gromacs/gromacs/runs/5583122334
Introduced in !2564 (merged) (5a5b1be1)
std::unary_function
has been deprecated in C++11, and has not been needed anyway.
Failed job: https://github.com/gromacs/gromacs/runs/5583122334
Introduced in !2564 (merged) (5a5b1be1)